The present invention relates to a hyperthermia apparatus or thermotherapy instrument of an ultrasonic heating system, and specifically relates to an improvement in an acoustic lens disposed in front of an ultrasonic vibrator.
In curing an affected body part having abnormal cellular tissue such as cancer or other tumor, it is clinically well known that heat treatment (hyperthermia), comprising heating the affected part in a temperature range of 43.degree. to 45.degree. C. for a dozen to several dozen minutes is effective as a treatment.
Conventionally, the heating is applied in a manner such that an ultrasonic heating region 7a is formed in the patient's body by controlling the phase using an annular vibrator (annular array) 4a as shown in FIG. 9.
However, as shown in FIG. 9, undesirable hot spots 7b are produced behind the heating region 7a by these prior art devices.
To eliminate such undesirable hot spots, an annular vibrator 4b (FIG. 10) is further divided in the radial direction as disclosed by Japanese Patent Application Laid-Open No. 42773/1987. In this arrangement undesirable hot spots are eliminated by dividing the heating region 7a into two parts and the phases of converged ultrasonic waves are inverse to each other at the position behind the heating region 7a where the undesirable hot spots are produced.
However, this proposed vibrator divided in the radial direction has deficiencies in that the structure of the vibrator is very complicated and the control apparatus whereto a delay circuit is added becomes complicated, resulting in high cost.